Using δ 15 N and δ 18 O Signatures to Evaluate Nitrate Sources and Transformations in Four Inflowing Rivers, North of Taihu Lake

摘要

Taihu Lake is the third largest freshwater lake in China. Due to rapid economic development and excessive nutrient discharges, there is serious eutrophication in the northern part of the lake. Nitrogen (N) is one of the key factors for eutrophication in Taihu Lake, which mainly comes from the rivers around the lake. Samples from four inflowing rivers were analysed for δ 15 N and δ 18 O isotopes in December 2013 to identify the different sources of nitrogen in the northern part of Taihu Lake. The results indicated that the water quality in Taihu Lake was clearly influenced by the water quality of the inflowing rivers and nitrate (NO 3 ? -N) was the main component of the soluble inorganic nitrogen in water. The soil organic N represented more than 70% of the total NO 3 ? -N loads in the Zhihugang. Domestic sewage was the major NO 3 ? -N source in the Liangxi river, with a contribution of greater than 50%. Soil organic N and domestic sewage, with contributions of more than 30% and 35% respectively, were the major NO 3 ? -N sources in the Lihe river and Daxigang river. Denitrification might be responsible for the shifting δ 15 N-NO 3 ? and δ 18 O-NO 3 ? values in the Daxigang river, and a mixing process may play a major role in N transformations in the Lihe river in winter. The results of this study will be useful as reference values for reducing NO 3 ? pollution in the inflowing rivers in the north of Taihu Lake.